Electron discharge device utilizing cavity resonators



7 2,445,077 ELECTRON DISCHARGE DEVICE UTILIZING July 13, 194 1.. s. NERGAARD ET AL v CAVITY RESONATORS 3 Sheets-Sheet 1 Filed June 25, 1942 ATTORNE Y L. s. NERGAARD ET AL ELECTRON DISCHARGE DEVICE UTILIZING July 13, 1948.

CAVITY RESONATORS 5 Sheets-Sheet 2 v Filed June 25, 1942 INVENTOR s 4'6. #5960094 0006. Ba /x9105 mm 4010.; PEA/86K www - A TORNEY July 13, 1948. s NERGAARD ET AL 2,445,077-

ELECTRON DISCHARGE DEVICE UTILIZING CAVITY RESONATORS 3 Sheets-Sheet 3 FiledJune 25, 1942 OufP -r INVENTORS AEO/YrS/Vffi flflPO, 0006. 501906705 mva 100/8 PEMS'HK A ORNE Patented July 13, 1948' ELECTRON DISCHARGE DEVICE UTILIZING CAVITY RESONATORS Leon S. Nergaard, Verona, and Don G. Burnside, East Orange, N. .L, and Louis Pensak, Brooklyn, N. Y., assignors to Radio Corporation of America, a corporation of Delaware Application June 25, 1942, Serial No. 448,382

21 Claims. (01. 315-65.

1 Our invention relates to electron discharge devices and circuits therefor, particularly useful at ultrahigh frequencies.

For certain applications electron discharge de-v vices must be operated as oscillators at ultra high frequencies. Under some conditions the device must also be capable of high peak power outputs for so-called pulse operation. Under these conditions of operation a number of problems are introduced, particularly where use is made of hollow conducting members referred to as resonant cavity circuits or'resonators, which circuits or resonators are themselves particularly efficient at ultra high frequencies. The resonators introduce complexities in the way of tube construction in coupling the electron discharge devices to the circuits, particularly in connection with electrode supports and seals in the envelopes of such devices. a

Electron discharge'devices of the kind under consideration normally utilize long electron beams directed through successive resonators from a cathode to a collector'normally main:

tained at a low voltage. Electron reflection due to space charge effects of the electrons in the beam results in undesired and uncontrolled feed back between the output and input circuits.

Electron reflection also results in increased space charge and lower current, and overheating of electrodes not intended to dissipate heat, such for example as the grid. Further, the power dissipated at the collector requires efiicient cooling since heating causes expansion, contraction and variation of interelectrode spacings which in turn affects the characteristics of the device. In addition this heating may severely affect the seals of the envelope made to the electrode supports and leads or to the electrodes themselves.

While the use of concentric lines and resonators forinput and output circuits offers the possibility of completely shielding one circuit from the other, their use introduces the problem of providing controlled feedback energy between the circuits in proper phase relationship and further presents the problem of providing proper insulating supportswhich will prevent voltage break-' down across the insulators. A ready means for determining the degree of coupling and hence the amount of feedback is also a problem in this type of tube. 1

In order to permit circuit and electrode combinations whereby different biasing voltages may be applied to the circuits and electrodes by-passing condensers must'be used which will prevent flash-over between the closely spaced electrodes and circuit elements during operation and mean for readily coupling the circuit elements to the tube elements must also be provided to insure rapid interchange of the electron discharge device in the apparatus when breakdown occurs.

An object of our invention is to provide an elec-.

tron discharge device which is suitable for use at I ultra high frequencies.

It is another object of our invention to provide a an electron discharge device which-is capable of pulse operation withhigh peak power output.

Another object of our invention is to provide an electron discharge device in which improved types of seals are utilized.

A further object of our invention is to provide an electrode structure whereby the interelectrocle spacing may be held uniform during operation of the electron discharge device.

A further objectof our invention is to provide an improved output electrode cooling system which is efficient and simple.

Another object of our invention is to provide an electron discharge device having input'and output circuits particularly suitable for ultra high frequencies, which are self-shielding and in which controlled coupling between the input and H output electrode systems can be accomplished in proper phase relationship.

Another object of our invention is to provide 7 a tube using improved circuits of the resonator type in which tuning, adjustment and coupling are simple and easily controlled from the outside, and in which feedbock control can behad without disturbing the radio frequency fields within the resonators.

Another object of our invention is to provide highfrequency apparatus of the type described 7 in which the electrodes and tank circuits may be maintained at widely different D.-C. potentials with the possibility of flash-over betweenv elements being reduced to a minimum.

A still further object of our invention is to provide a mechanical coupling arrangement between the circuits and the electrodes of the electron discharge device proper which can be easily made and which will insure proper contact.

A further object of our invention is to provide an apparatus for ultra high frequency use which is simple in construction, easy to assemble and in which the exposed parts for the. most part are at ground potential.

Another object of our invention is to provide ready means for coupling the electron discharge device with the circuit elements to insure inter 1 is a longitudinal section of the ultra high frequency apparatus made according to our invention, Figure 2 is a section taken along the line 2-2 of Figure 1, Figure 3 is a section taken along the line 3--3 of Figure 1, Figure 4 shows details of construction of Figure 2, Figure 5 shows the details of one ring support for the cathode, Figure 6 is a longitudinal section of the electrode structure and envelope seals of the electron discharge device made according to our invention and used in the apparatus shown in Figure 1, and Figure 7 7 is a schematic diagram. of the apparatus made according. to our invention and shown in Figure l'.

Figure 1. shows an ultra, high frequency apparatus incorporating our invention. The electron discharge device includes an evacuated envelope Iilhaving successively positioned along'its longitudinalaXis a cathode H, supported on the ring l2 and grid l3 supported on ring M, these rings being sealed through the envelope wall. The end of the envelope Iii! is closed by the anode or collector I5, which projects beyond the envelope and has secured to it the cooling. radiator IE, to which the anode voltage leadll isconnected. Leads I8 provide the heating current for the indirectly heated cathode and the lead I?! is electrically connected to the cathode ring in a manner to be described.

circumference with flexible fingers 5o slidably engaging the inner tubular member 35 but spaced from the outer tubular member to permit communication between the two spaces on either side of the device for tuning. Longitudinal movement of this tuning collar or member is accomplished by means of the rod 39 extending outside the hollow conducting member or input circuit.

The output tank circuit comprises a pair of telescoping cup-shaped members El, 52, which form together a drum-like resonator. The cupshaped'member 5! is electrically connected to and engages the Ufshaped collar 4|. Member 52 is provided with the collar member 66 having an ,L-shaped section which performs a function to be described. The cup-shaped member 52 may be telescoped within the member 5| and engagement between the'two members is insured by meansof flexible fingers 53 on member 52. Relative axial movement of the two members to vary the axial dimension of the resonator is accomplished by means of the structure best shown in Figures 2 and 4. Screw members 54 rotatably supported in bracket elements .55 on member 52 engage threaded brackets 56 mounted on the cupshaped member 5|. By-rotating the screw members the space between the cup-shaped members The electron discharge device which is to be I conducting member er, At the open end of the inner tubular member 35 is mounted a collarshaped member 38 provided with a plurality of outwardly flared resilient fingers 39' which contact with the cathode ring seal $2. This collarshaped member 38 is clamped to the end of the tubular member 35 but insulated therefrom by insulating collar Ml, preferabl of mica. Because of this construction the cathode may be maintained. at a. different D.-C. potential from the inputcircuit and grid by means of the conductor l9 electrically connected to the collar 38 at IS. The outer tubular member 36 is received within a U-shaped collar member 4| to which the collar member 42 is secured at :23. This gives the resilient fingers 42' a. relatively long flexible length for engaging the grid ring Id. Thus there is provided between the grid and the cathode a hollow resonant conducting member totally enclosing and confining any radio frequency fields generated between the cathode and the grid.

Slidably mounted between the two tubular members 35 and 36 is the ring member 45 .provided with flexible fingers 45 and 41 engaging, respectively, the inner and outer tubular members 35 and 36. This ring is initially positioned to determine the frequency range of operation of the input circuit, tuning being accomplished by means of the member 48 provided on its inner 5| and 52 may be increased or decreased to vary the output frequency of operation of the resonator. i

The flange collar Gil shown in Figure 1 secured to the cup-shaped member 52 is capacity coupled to the collar 6| through insulating collar 62 preferably of mica and extending for some distance on either side of the members 66 and 6!. The member BI is provided with a plurality of-fi'exible fingers 53 for engaging the collar 39 electrically connected to the anode and forming part of the wall of the output resonator. Thus there is provided an enclosed space between the grid and the anode which is self-shielded from the enclosed space between-'the'cathode andthe grid. Energy may be taken out of the o-utput resonator by means of the coupling loop 65 having its opposite ends connected to the inner member 66 and outer member 61 of the coaxial transmission line. A cooling medium may be directed within the output resonator and against the seals through the ducts 68 and 69.

In order to couple the input and output circuits to control the amount of energy transferred between the circuits, we provide an adjust-able coupling loop and a variable transmission line coupled between the two resonators. The transmission line connecting: the: input and output resonators includes a hollow conducting box-like member T0 opening into the box-like member provided with spaced partition walls 12 so that a U-shaped passageway is provided within the box-like member. An elongated box-like structure 13 between the input resonatorand the member H provides another passage through which the transmission line extends. The inner conductor of the shielded transmission line coma dielectric constant of approximately one. We have found that insulators having a higher dielectrio constant cause discontinuities in the surge impedance of the line, which in some cases results in breakdown through the insulation. 7 By means of our construction, this breakdown is substantially eliminated. J

One end of the, conductor Ilisconnected to the coupling .loop 16 rotatably mounted on rotatable shaft 15 best 'shown'in Figures ,1 and 2. Rota.- tion of shaft 15 increases or decreases the radius of the loop to vary coupling with the radiofre-v quency field within the resonator. The other end of the transmission lineis connected toa stub 85 of the L-shaped member 84. The member 84 has at its other end ,a split elementilli for engaging the inner tubular member 35, this member extending through a slot 35". in member 36. Movement of this element 84 with respect to the resonator isaccomplished by means of a rod 81 to vary theipoint at which the connection is made to the interior of the resonator to provide the coupling desired. Thusthe amount ofcoupling can be varied to determine the amount of energy to be fed back to the input circuit. The phase relationship between the energy fed back to the input circuit and the input voltage can be determined by'the length of the transmission line and the position of member 84 within the input circuit.

-In Figure. 3 can be seen the details of the transmission'line and the connecting element with respect .to the input resonator.

Detailsof the electrode structures and seals are shown in Figure 6. The cathode includes the collar member 20 connected to ring l2 by'means of the radially directed conductors 2|, the emitting portion 23 of the cathode beingsupported from the collar by means of the conductors 22 arranged in a circle and connectedto collar 20.

The heater leads l8 liewithin thisicollar and are electrically shielded by the conductors 21 and'22- of this cathode construction and the inner tubular member 35 of the input'circuit.

To insure a fixed spacing between the grid and cathode the grid is positioned with respect to the cathode by means of the insulating bead construction 26 connected to the'cathode collar 20 and the apertured cup member 24; the grid being electrically connected to the grid ring M by means of the L-shaped conductors 25. The member 24 and ring seal I4 provide with the input resonator a self-shielded input circuit equivalent to a solid wall hollow resonant conducting member. The grid and cathode maybe assembled as a unit before being incorporated in the envelope. a

.In Figure is shown more indetail the ringlike conducting members secured to the cathode and grid for supporting the grid and cathode and for providing a means of contact between the resonators and theelectrodes within the glass envelope. Thering I2 is provided on-the outside edge with a series of radially positioned slots l2 which may be enlarged at the inner end as shown and on the inside edge with slots l2". This arrangement avoids stresses and strains in the ring due to heat absorption and thus prevents warping and strains on the seals.

The anode I5 is provided with an electron receiving surface having the same relative shape as the'cathode andgrid and it is found that the concave surfaces of thegrid and cathode pro vide a more nearly fixed spacing than other forms since anycontraction or expansion causes;

direction. By placing the anode close to the grid and cathode, long beams are avoided and space charge reflection is eliminated. The high anode voltages used result in considerable heating which requires means, for dissipating the heat rapidly to avoid grid emission caused by the grid absorbing heat from theanode. and to keep the anode at a safe operating temperature.

In accordance with our invention we'provide the anode with a cone-shaped cavity 21 within the extended portion of the anode to which the radially extending cooling fins [6 are secured. Withthis arrangement the large mass of anode adjacent the receiving surface absorbs and quickly transmits the heat to an effectively long and large area radiating surface, thus quickly disposing of any heat generated at-thereceiving suriaceof the anode. I

To insure that the anode seal will be effectively protected during manufacture and during operation an annular depression 28 is provided having a reentrant collar 28' surrounding the depression and to which the outwardly flared collar 29 is secured, the thickness of the collar 28' and collar 29 being substantially the same to permit expansion and contraction due to variation of heating to be of the same degree so as to'insure proper sealing. The end of the collar 29 is rounded to provide a proper seal in the glass envelope I0. Thus, a long path of comparatively low conductivity for heat from the receiving surface of the anode or collector to the seal is provided which offers considerably more resistance to the flow of heat than does the more solid portion of the anode through which the heat is conducted to the radiating fins l6.

A schematic longitudinal section of the apparatusmade according to our invention and the associated circuits and voltage sources is shown in Figure 7. The cathode heater may be energizedfor preventing the modulation currents from flowing through the meter. The usual protective bleeder resistors areshown. The resonators are maintained at ground potential by means of conductors 9| and 92 connected to ground. Theinput pulse or modulating signal is applied to the cathode by means of conductor 94, the resistors 95 and 96 determining the bias on the grid'relative to the cathode. Normally the grid is biased to cut-off by resistors 95-416 and the bias voltage neutralized by a pulse voltage being applied to the grid l3. This permits a flow of current for a short period of time between the cathode and anode. The output resonator formed of cup-shaped members 5| and 52 is thus excited and energy fed back into the input resonator by means of coupling loop 16 and transmission lines high peak power outputs. The input and output circuits are particularly suitable for use at ultra high frequency and are self-shielding. The coupling between the input and output electrode systems can be substantially absolutely controlled, and feedback with proper phase is thus assured.

Adjustments are simple-and; easily controlled from the outside ofthe apparatusand feedback may be controlled without disturbing the radio frequency fields within the resonators. The construction utilized provides sure seals and yet at the same time permits the use of leads and supports which can be readily coupled toresonators. The electrode construction assures constant electrode spacing during operation of the electron discharge device and the collector construction and cooling system maintains the collector at a safe operating temperature and reduces grid heat absorption and emission. The construction used for providing capacity coupling between elements atdiiferent dire-ct potentials and for insulatingly supporting the elements within the apparatus reduces the possibilities :of flash-over and leakage. The construction utilized by our invention permits the substitution of one electron discharge device for another to be made readily and speedily. These and other objects enumerated above are attained by applicants invention.

While we have indicated the preferred embodiments of our invention of which We are now aware and have also indicated only one specific application for which our invention may be employed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims.

What we claim as new is:

1. An electron discharge device including a cathode for supplying electrons and a collector for receiving said electrons, and a control electrode positioned between said cathode and collector, said cathode, collector and control electrode having ring-like conductors and hollo'wresonant conducting members provided with expandable coupling elements engaging said ring like conductors and providing self-shielded circuits between the cathode and control electrode and between tho-control electrode and collector and means for transferring energy between the hollow resonant conducting members and including a coupling loop in one of said hollow resonant conducting members and an adjustable concentric transmission line having an inner conductor, one end of which is connected to. said coupling loop and its other end extending within.

and coupled to the inner surface of the other hollow resonant conducting member, the outer conductor of said, transmission line being electrically connected to said hollow resonant conducting members.

2. An electron discharge device having a cathode, control electrode and collector all in fixed relative positions, radially directed conductors connected to said control electrode and collector and 'an output resonator electrically coupled between the radialconductors of the control electrode and collector and including a pair of telescoping cup-shaped members, and means for varying the relative position of said cup-shaped members to vary the natural frequency of oscillation of the resonator, said resonator having flexible finger-like elements engaging the radially directed conductors, said means for varying the relative position of said telescoping cupshaped members including adjustingscrews supported on the exterior of said telescoping cupshaped members.

3. An electron discharge device havingia cathode, control'electrode and collector, said control electrode and collector having ring-like conductors'and an output resonator electrically coupled between the ring-like conductors and including a pair of telescoping cup-shaped members, and means on said resonator for varying the relative position of said'cup-shaped members .to vary the natural frequency of oscillation of the resonator, one of said cup-shaped members having flexible finger-like elements engaging one of said ring-like conductors, the other of said cup-shaped members having an annular member, a second annular member within the first mentioned annular member and capacitively coupled thereto and having flexible finger engaging the other ring-like conductor.

4. An electron discharge device having'a cathode, control electrode and collector, said control electrode. and collector having ring-like conductors and an output :resonator electrically coupled between the ring-like conductors, one portion of said resonator having flexible finger-like elements engaging .one of said ring-like conductors, another portion of said resonator having ,a first annular member, a second annular member within said i'irst .annular member and capacitively coupled to said first annular member and having fingers engaging the other ring-like conductor, whereby the space between the ring-like conductors communicates with the interior of said resonator.

5. An electron discharge device having a'cathode, and an anode, said :anode comprising an elongated hollow member defining a cavity therewithin and having a closed end for receiving electrons and an open end being open :to the exterior of said device, said closed end being closest to said cathode, the cavity within said hollow member extending from, the open end thereof and of decreasing proportions towardsaid closed end and radiating fins positioned transversely of and successively along said anode from the open end toward the closedend.

6. An electron discharge device having an envelope containing a cathode, and an anode, aid anode comprising an elongated hollow'member, one end of which is closed and oppositely disposed to said cathode within said envelope to receive electrons from the cathode the cavity within said anode extendingf-rom the open end thereof and of decreasing proportions toward the end for receiving electrons, and heat radiating means positioned on said anode, said cavity :being open to the exterior of the envelope.

7. vAn electron discharge device having a cathode, control, electrode and anode, said cathode, control electrode and anode having registering concave surfaces spaced from each other, said anode comprising an elongated member having its concave end positioned to receive electrons from said cathode and having -a cone-like cavity extending :from the other end thereof with the tip of the cone toward the concave end for receiving electrons, and heat radiating fins positioned transversely of and successively alon said anode.

8. An electron discharge device having an envelope containing a cathode, and an anode, said anode being elongated and having one end within said envelope and oppositely disposed to said cathode to receive electrons from said cathode and having a cone-likev cavity extending from the other end thereof with the tip of the cone toward the end for receiving electrons, and a collar member electrically connected to and supported onlsaid anode intermediate the ends 01' the anode, said collar member extending along the anode but spaced therefrom and having the free edge of said collar sealed to one end of said envelope, and heat radiating means positioned said anode, and an annular lip on said anode extending around and along the anode and having one edge spaced from said anode and extending toward the receiving end of said anode, an outwardly flared collar member having one end secured to said lip and the other end sealed to said envelope closing the end of said envelope, and heat radiatin fins extending transversely of the anode, and positioned successively along the anode outside of said envelope.

1: 10.; An electron-discharge device having a cathode provided with a ring-like supporting element, and an, anode, said anode being elongatedand having one end within said envelope and oppositely disposed to said cathode to provide a surface for receiving electrons from the cathode, said anode having a cone-like cavity extending from the other end thereof with the tip of the cone toward the end for receiving electrons, and a collar member having one end secured to the anode intermediate the ends of said anode and flaring outwardly toward the receiving end of the anode, and insulating material connected between the ring-like member of said cathode and the free end of said collar member providing an envelope for said cathode and said anode, and heat radiating fins connected to said anode exteriorly of the envelope of said tube.

11. An electron discharge device including an envelope having a cathode, grid electrode and'an anode, said cathode and grid electrode including a pair of nested cup-like elements insulatingly supported from each other and having radially directed supporting elements, ring-like supporting elements coaxial with said cathode and grid electrode'and electrically connected to said radially directed supporting elements and sealed through'the wall of said. envelope, said anode having a collar member, one edge of which is connected to the anode and the other edge of which is sealed to the end of the envelope providing an enclosure for said cathode, grid electrode and anode.

12. An electron discharge device having a cathode, grid and anode, said cathode and grid being provided with coaxial ring-like conducting members supporting said cathode and grid, and a collar on said anode coaxial with said ring-like members, an input circuit including a coaxial line resonator, the inner conductor of said resonator being provided with longitudinally extending flexible conducting fingers engaging the periphery of the cathode ring-like member, and the outer conductor of said resonator being provided with other longitudinally extending flexible conducting fingers engaging the periphery of the grid ring-like member, whereby the space between the cathode and grid communicates with the interior of said resonator, and a resonator coupled between said first resonator and said 10 anode and having a plurality of longitudinally extending flexible fingers electrically contacting the periphery of said collar.

13. An electron discharge device having a cathode, grid and anode, said cathode and grid being provided with coaxial ring-like conducting members supporting said cathode and grid, and a collar on said anode coaxial with said ring-like members, a coaxial line resonator, the inner conductor of said resonator bein provided with longitudinally extending flexible conducting fingers engaging the periphery of the cathode ring-like member, and the outer conductor of said resonator having longitudinally extending flexible conducting fingers engaging the periphery of the grid ring-like member, whereby the space between the cathode and grid communicates with the interior of said resonator, and a resonator coupled between said first resonator and said anode and having a plurality of longitudinally extending flexible fingers electrically contacting said collar, and a coaxial transmissionline coupling the resonators.

14. An electron discharge device havinga cathode, grid and anode, said cathode and grid being provided with coaxial ring-like conducting members supporting said grid and cathode, an input coaxial line resonator, the innerconductor of said resonator having flexible conducting fingers engaging the cathode ring-like member, and the outer conductor of said resonator having flexible conducting fingers engaging the grid ring-like member, whereby the space between the cathode and grid communicates with the interior of said resonator, and a second resonator coupled between said first resonator and said anode, and a coaxial transmission line coupling the resonators together, a coupling'loop within'said second resonator and connected to one end of said line, and a contact member connected to the other end of said line, said contactmember being movable along and contacting the inner surface of the inner conductor of the input resonator.

15. An electron discharge devicehaving an envelope containing a plurality 'of electrodes and a ring-like supporting element extending through said envelope and electrically connected toone of said electrodes, said ring-like member being sealed through the wall of the envelope of the tube and having radial slots therein extending from an edge of said ring-like member.

16. An electron discharge device having'an envelope containing a plurality of electrodes and a ring-like supporting element extending through said envelope and electrically connected to one of said electrodes, said ring-like member being sealed to the wall of the envelope and having a plurality of radial slots therein extending from opposite edges thereof.

17. An electron discharge device having an envelope containing a plurality of electrodes and. a ring-like supporting element extending through said envelope and electrically connected to one of said electrodes, said ring-like member being sealed to the wall of the envelope and having radial slots therein extending from the outer edge toward the inner edge of said ring-like member exteriorly of the envelope and being enlarged at their inner ends.

18. An electron discharge having a cathode, control electrode and anode, a first resonator connected between said cathode and control electrade, and a second resonator connected between said control electrode and anode, and a coaxial transmission line connected between said resonators, one end of said coaxial transmission line extending Within said first resonator and a coupling loop within said second resonatorconnected to the other end of said transmission line, said coupling loop including an arcuate-shaped flexible member and means connected to saidarcuate-shaped flexible member for changing the radiusof curvature of said flexible member to vary the coupling of said loop with said second resonator.

19. An electron discharge device having a-cath ode, control electrode and anode, a resonator connected between said cathode and control electrode, and a second resonator connected between said control electrode and said anode, an adjustable coaxial transmission line coupled between said resonator and'including an elongated tubular structure having a longitudinally adjustable partition providing a pair of adjacent passageways of adjustable length communicating at one end and an inner conducting member supported Within said passageways and adjustable with said partition to change the length of said transmission line, and a coupling 100p connected to one end of said transmission line and within one of said resonators, and a tap connected to the other end of said transmission line and extending within the other resonator.

20. An electron discharge device having a cathode, control electrode and anode, a first resonator connected between said cathode and control electrode, and a second resonator connected between said control electrode and said anode, and a coaxial transmission line connected between said resonators and including an elongated tubular structure, a partition extending along said tubular structure providing a pair of adjacent parallel chambers having a communicating passageway at one end, a tubular member Within each of said chambers and extending longitudinally of said chambers but out of contact with the tubular structure and a U-shaped element telescopically engaging and connecting said tubular members and extending through said communicating passageway, a partition extension, said partition extension and said U -shaped member being movable as a unit t vary the length of the coaxial transmission line, a coupling loop within said second resonator and'connected to one of said tubular members, and a contact member within the first resonator and connected to the other tubular member.

21. An electron discharge device having a cathode, control electrode and anode, a first resonator connected between said cathode and control electrode, and a second resonator connected between said control electrode and said anode, and a coaxial transmission line coupling said resonators and including an elongated tubular conducting structure, a partition Within said structure dividing the tubular structure into two chambers having a communicating passage at one end and comprising a pair of closely spaced elements, a first member positioned longitudinal- 1y of and out of contact with the walls of one of the chambers and a second member positioned longitudinally of and spaced from the Walls of the other chamber, a U-shaped member having its ends telescopically engaged with said members and slidable with respect to said members, an elongated member slidabl engaged between the spaced partition elements for extending the length of said partition within the tubular structure and movable means closing one end of said tubular structure adjacent the U-shaped element, said closure member, U-shaped member and slidable elongated member being movable as a unit longitudinally f the tubular structure to vary the length of the transmission line, one of said tubular elements being electrically connected to the interior of the first resonator and the other tubular member being coupled to said second resonator.

LEON S. NERGAARD.

DON G. BURNSIDE.

LOUIS PENSAK.

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